ABSTRACT / PROJECT SUMMARY Diabetic kidney disease (DKD), the leading driver of the global burden of kidney disease, is resistant to most treatment options. Thus, development of effective therapies to slow the progression of DKD is crucial. Mesenchymal stromal cells (MSC), approved for treating refractory inflammatory diseases elsewhere, possess paracrine anti-fibrotic, anti-apoptotic, pro-angiogenic and immunomodulatory regenerative activities, offering hope for DKD. Interim analyses from our Phase I clinical trial delivering patient-derived MSC in non- diabetic renovascular disease demonstrated safety, preserved kidney function, and improved kidney blood flow. In experimental DKD, MSC decrease glomerulosclerosis, microalbuminuria, inflammation and fibrosis. We wish to test the potential of patient-derived MSC therapy to minimize the risk of allosensitization or cell destruction with allogeneic stem cell treatment approaches. However, MSC from individuals with DKD may function suboptimally due to senescence. Cellular senescence, an irreversible arrest of cell proliferation, is induced by DNA damage and promotes inflammation, contributing to tissue injury and cell dysfunction. In our Phase I randomized, open label trial, we are currently testing the safety and efficacy of senolytics, drugs that clear senescent cells, to repair the health of MSC in individuals with DKD. Preliminary studies show reductions in senescent adipose cells and improved MSC function. However, it remains unclear whether these changes affect MSC reparative capacity on injured renal cells or in DKD. Our long-term goal is to promote the development of a novel cell-based therapy for DKD. We hypothesize that senolytic agents taken by subjects with DKD will improve the renal repair capacity of the patient?s own MSC, by enhancing anti- inflammatory, anti-fibrotic and pro-angiogenic paracrine activities. Using adipose-derived MSCs harvested from subjects with advanced DKD (eGFR 15-45 ml/min/1.73m2) in the ongoing senolytic therapy trial, the proposed project will: (1) Test the hypothesis that DKD MSCs from subjects treated in vivo with senolytics (SenDKD-MSC) will achieve greater reduction in inflammation and epithelial-to-mesenchymal transition (EMT) program in injured renal tubule epithelial cells (TEC) in vitro, via paracrine-mediated actions, as compared to untreated DKD-MSC. (2) Test the hypothesis that SenDKD-MSC infusion will exhibit greater potency vs. DKD-MSC in the repair of mouse kidneys in vivo, by reducing albuminuria, fibrosis, hypoxia, and inflammation in experimental DKD with angiotensin II-induced hypertension. These pilot studies will allow the assessment of senolytic-induced MSC renal repair effects in experimental DKD and enhance successful testing of a novel, senolytic MSC preconditioning strategy in human DKD. Significance and Impact: Cell-based therapy to delay DKD progression is very promising. Senolytic therapy may improve stem cell function and multiple aging-related conditions. Unravelling the mechanisms by which these novel interventions may work to synergistically regenerate the diabetic kidney could lead to successful large-scale clinical trials in the future.